Hydrogen is an ultimate clean energy source which, unlike fossil fuels, is burnt without evolution of any substances that is liable to pose the environmental problem, such as carbondioxide gas and sulfur oxides, and, delivering a heat quantity per unit mass three times or more greater than petroleum oils, and when supplied to fuel cells, can be converted into electric and thermal energies with a high degree of efficiency.
As a conventional chemical process for production of hydrogen, for example, there have been proposed several technologies, inclusive of the thermal-cracking or steam reforming process of natural gas or naphtha. These production technologies need the severe reaction conditions of high temperature and high pressure, while they yield the synthesis gas containing CO (carbon monoxide), and such gas, on the occasion of utilization in fuel cells, is consequently required to be freed of CO to circumvent the problem of poisoning of fuel-cell electrode catalysts. However, the removal of CO involves technological difficulties, and is not easy to accomplish.
On the other hand, the method of biological hydrogen generation by microorganisms proceeds under the mild reaction conditions of ambient temperature and atmospheric pressure, and generates the gas, which does not contain CO, without being required to remove the same.
From such viewpoints, the method of biological hydrogen generation with use of microorganisms is attracting enhanced attention as a more preferred means of supplying a fuel intended for use in fuel cells.
The method of biological hydrogen generation is roughly classified into the two methods: the method using a photosynthetic microorganism and the method with use of a non-photosynthetic microorganism (mainly anaerobic microorganisms).
The former method, although it utilizes the energy of light for generation of hydrogen, needs a vast light-capturing surface area because of its low utilization efficiency of the light energy, and encounters lots of the problems left to be solved, such as the expensive cost investment requirement for the hydrogen generation facilities and difficulties in securing its maintenance, thus still remaining far from the commercially practical level.
With reference to the latter method, there have been known the various metabolic pathways being responsible for generating hydrogen by the anaerobic microorganisms. Such metabolic pathways include, for example, the pathway of generating hydrogen during the step of break-down of glucose to pyruvic acid; the pathway of generating hydrogen during the step of production of acetic acid from pyruvic acid via acetyl CoA; and the pathway of generating hydrogen directly from formic acid derived from pyruvic acid, and the like.
Among these, the pathway of generating hydrogen directly from formic acid derived from pyruvic acid is working by lots of microorganisms as the FHL system.
Referring to the FHL system, a report was published on Escherichia coli. With regard to the FHL system of Escherichia coli, however, there was proposed a model structural assembly indicating a complex consisting of numerous, extremely complex enzymatic proteins, but there has not yet been clarified the whole aspects of gene groups encoding the enzymatic proteins involved in generation of hydrogen (refer to Sauter, M., et al., Molecular Microbiology, 1992, vol. 6, p. 1523-1532).
With reference to the function of the FHL system, on the other hand, the fhlA gene has been analyzed to be identified as a transcription activator gene for the gene encoding part of the enzymatic proteins constructing the FHL complex (Schlensog, V., et al., Molecular Microbiology, 1990, vol. 4, p. 1319-1327).
The present invention also relates to a technique of inactivating the hycA gene. It was shown by Penfold, D. W. et al. (Enzyme and Microbial Technology, 2003, vol. 33, p. 185-189) that an Escherichia coli strain being deficient in the hycA gene exhibits an improved hydrogen-generation capability from saccharides, such as glucose, as compared with its wild strain, but no mention was made about the fhlA gene. There has not been known so far in the past that the microorganism, which possesses the FHL system having undergone to transformation in terms of the fhlA and hycA genes as identified in the present invention out of a group of the genes involved in the formation of the FHL system, or a conjugated body of complex enzymatic proteins, can acquire the outstandingly improved function to generate hydrogen from formic acid.